Green had the distinction of being the first black player to play for the Red Sox, the last pre-expansion major-league club to integrate. In his Boston tenure, he was used mostly as a pinch runner or day-off replacement for infielders Pete Runnels and Don Buddin. He made his debut on July 21, 1959, pinch-running in a 2-1 loss against the White Sox.

Since major-league baseball had not yet expanded to the West Coast, Green grew up a fan of the Oakland Oaks of the Pacific Coast League. Green later stated that he may have been even better at basketball, but chose to play baseball when he was offered a baseball scholarship at Fresno State University. However, Green decided to attend Contra Costa College when Gene Corr, his high school baseball coach, became the baseball coach there and promised Green he would play shortstop if he attended.[2] In Green's final year of college, he tried out for the Oaks, and was signed to a contract.

In 1959, Green was invited to the Red Sox's major league spring training camp. Despite playing well and receiving much media attention, Green was sent back to Minneapolis. However, after hitting .320 through 98 games, he was promoted to the major league Red Sox on July 21, 1959.[3][4]

Green made his debut as a pinch runner against the Chicago White Sox at Comiskey Park. He also started the next game at second base, going 0-for-3. His first at bat at Fenway was a triple off the Green Monster. One week after Green's debut, pitcher Earl Wilson was called up, becoming the Red Sox's second black player. Green would play 50 games during the 1959 season, batting .233 and playing second base almost exclusively.[4]

Green enjoyed a much more full-time role in 1960, playing 133 games, 69 at second base and 41 at shortstop.[4]

Green may have had his best season in 1961, posting career highs in home runs (6), RBI (27), doubles (12), and stolen bases (4), although he also had the most errors of his career that year, with 16. Despite a hot start to the season, Green developed an appendicitis in Washington, D.C. in May, which put him out of the lineup for about four weeks, and kept him from playing at full strength for even longer.[2]

After the 1962 season, Green was traded to the New York Mets along with Tracy Stallard and Al Moran in exchange for Felix Mantilla. Green played the majority of the 1963 season with the Buffalo Bisons, but also played 17 games with the Mets. He played his final major league game with the Mets on September 26, 1963, although Green would play two more seasons in the minor leagues before retiring after the 1965 season.[3] In a five-season major league career, Green was a .246 hitter with 13 home runs and 74 RBI in 344 games.[4]

On April 17, 2009, Green was honored by the Red Sox in a first-pitch ceremony, in recognition of 50 years since his breaking of the Red Sox color barrier.[7] In February 2012, Green was honored by the city of El Cerrito, and presented with a proclamation honoring his "distinguished stature in baseball history."[6] In April 2012, he threw out the ceremonial first pitch before Jackie Robinson day at Fenway Park, and also attended Fenway's 100th anniversary celebrations later that month.[8][9]